• 대한화학회지
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• 제55권2호
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• pp.317-322
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• 2011

• Nuclear Engineering and Technology
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• 제53권8호
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• pp.2454-2463
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• 2021

The objective of this research is to the use of americium (AmO₂) as a burnable absorber effectively instead of conventional gadolinium (Gd₂O₃) for VVER-1200 reactor by analyzing its impacts on reactivity, power peaking factor (PPF), safety factor, and quality of the spent fuel. The assembly is burned to 60 GWd/t by using SRAC-2006 code and JENDL-4.0 data library for finding the optimum amount and effective way of using AmO₂ as a burnable absorber. From these studies, it is found that AmO₂ can decrease the excess reactivity like Gd₂O₃ without changing the criticality life span and enrichment of ²³⁵U. A homogeneous mixture of the 0.20% AmO₂+ 4.95% enriched UO₂ fuel rod (model MF-4) decreases the PPF than the reference assembly. The use of AmO₂+UO₂ in the integral burnable absorber (IBA) rod or the outer layer could also decrease the PPF up to 10 GWd/t but increases rapidly after 30 GWd/t, which could be a safety threat. The fuel temperature coefficient and void coefficient of the model MF-4 are the same as the reference assembly. In addition, 22% of initially loaded Am are burning effectively and contributing to the power production.

• 한국분말재료학회지
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• 제14권1호
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• pp.8-12
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• 2007

The effect of a CAM (Continuous Attrition Mill) treatment on the sinterability of ex-ADU $UO_2$ powder was investigated. As the cycles of a CAM increased, the apparent density, specific surface area and O/U of the milled powder increased, but there particle sizes decreased. However the sintered density of the $UO_2$ pellet decreased as the cycles of the CAM increased. It is considered that the decrease of the sintered density is due to the formation of $U_3O_8$, which was produced by a CAM mechanism.

• Nuclear Engineering and Technology
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• 제46권6호
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• pp.863-868
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• 2014

The evaluation of thermal properties of actinide oxide fuels is a problem of high importance for the development of new generation reactors. In the present study, an expression obtained for n-dimensional Debye functions is used to derive a simple analytical expression for the specific heat capacity of nuclear fuels. To test the validity and reliability of this expression, the analytical expression is applied to $UO_2$, $NpO_2$, $ThO_2$, and $PuO_2$. It is seen that the formula was in agreement with the experimental and theoretical results reported in the literature.

• Nuclear Engineering and Technology
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• 제52권4호
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• pp.674-680
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• 2020

We used MCNP6 computer code to model HTR-10 core reactor. We used two types of fuel; UO₂ and (Th+Pu)O₂ mixture. We determined the critical height at which the reactor approached criticality in both two cases. The neutronic and burnup parameters were investigated. The results indicated that the core fueled with mixed (Th+Pu)O₂, achieved about 24% higher fuel cycle length than the UO₂ case. It also enhanced safeguard security by burning Pu isotopes. The results were compared with previously published papers and good agreements were found.

• 한국세라믹학회지
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• 제41권11호
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• pp.797-803
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• 2004

마이크로파 가열장치를 이용하여 마이크로파 조사에 따른 SiC와 MO$_2$ 시료에 대한 발열실험을 수행하였고, 이 실험에서 얻은 발열특성 결과들을 고려하여 $UO_2$+5wt% CeO$_2$ 성형체에 대한 산화소결 실험을 수행하였다. 그리고 마이크로파와 전기로에서 각각 소결된 MO$_2$ 소결체의 특성변화를 비교분석하였다 마이크로파 조사에 따른 MO$_2$시료의 발열온도는 입력전력의 증가에 따라서 급속히 증가하였으며, 출력전력은 주로 보조가열재인 SiC와 MO$_2$ 시료가 마이크로파와 반응하는 정도에 따라서 변하였다. 마이크로파에 의하여 소결된 소결체의 밀도는 전기로에서 동일한 조건으로 소결된 소결체의 밀도보다 약 2% T.D. 낮았다. 소결체의 미세조직은 전기로에서 제조된 소결조직에 비하여 마이크로파에 의해 제조된 소결체의 기공분포가 불규칙적이었으나, 평균결정립 크기는 크게 나타났다.

• Nuclear Engineering and Technology
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• 제41권6호
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• pp.867-874
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• 2009

Solubility of a radionuclide is important for defining the release source term of a radioactive waste in the safety and performance assessments of a radioactive waste repository. When the pH and redox potential of the KURT groundwater were changed by an electrical method, the concentrations of uranium and thorium released from $UO_2$(cr) and $ThO_2$(cr) at alkali pH(8.1 ${\sim}$ 11.4) and reducing potential (Eh < -0.2 V) conditions were less than $10^{-7}mole/L$. Unexpectedly, the concentration of tetravalent thorium is slightly higher than that of uranium at pH = 8.1 and Eh= -0.2 V conditions, and this difference may be due to the formation of hydroxide-carbonate complex ions. When $UO_2$(s) and $UO_2$(am, hyd.), and $ThO_2$(s) and $Th(OH)_4(am)$ were assumed as solubility limiting solid phases, the concentrations of uranium and thorium in the KURT groundwater calculated by the PHREEQC code were comparable to the experimental results. The dominating aqueous species of uranium and thorium were presumed as $UO_2(CO_3)_3^{4-}$ and $Th(OH)_3CO_3^-$ at pH = 8.1 ${\sim}$ 9.8, and $UO_2(OH)_3^-$ and $Th(OH)_4(aq)$ at pH = 11.4.

• Nuclear Engineering and Technology
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• 제46권1호
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• pp.117-124
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• 2014

The effect of various process variables on the powder properties of recycled $U_3O_8$ from MnO-$Al_2O_3$ doped large grain $UO_2$ pellets and the effect of those recycled $U_3O_8$ powders on the sintered density and grain size of MnO-$Al_2O_3$ doped large grain $UO_2$ pellets have been investigated. The evolution of morphology, size, and BET surface area of the recycled $U_3O_8$ powders according to the respective variation of the thermo-mechanical treatment variables of oxidation temperature, powder milling, and sequential cyclic heat treatment of oxidation and then reduction was examined. The correlation between the BET surface area of recycled $U_3O_8$ powder and the sintered pellet properties of MnO-$Al_2O_3$ doped pellets showed that the pellet density and grain size of doped pellets were increased and then saturated by increasing the BET surface area of the recycled $U_3O_8$ powder. The density and grain size of the pellets were maximized when the BET surface area of the recycled $U_3O_8$ powder was in the vicinity of $3m^2/g$. Among the process variables applied in this study, the cyclic heat treatment followed by low temperature oxidation was a potential process combination to obtain the sinter-active $U_3O_8$ powder.

• 방사성폐기물학회지
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• 제20권2호
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• pp.193-207
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• 2022

Thermodynamically, TRUO_x, REO_x, and SrO_x can be chlorinated using ammonium chloride (NH₄Cl) as a chlorinating agent, whereas uranium oxides (U₃O₈ and UO₂) remain in the oxide form. In the preliminary experiments of this study, U₃O₈ and CeO₂ are reacted separately with NH₄Cl at 623 K in a sealed reactor. CeO₂ is highly reactive with NH₄Cl and becomes chlorinated into CeCl₃. The chlorination yield ranges from 96% to 100%. By contrast, U₃O₈ remains as UO₂ even after chlorination. We produced U/REO_x- and U/SrO_x-simulated fuels to understand the chlorination characteristics of the oxide compounds. Each simulated fuel is chlorinated with NH₄Cl, and the products are dissolved in LiCl-KCl salt to separate the oxide compounds from the chloride salt. The oxide compounds precipitate at the bottom. The precipitate and salt phases are sampled and analyzed via X-ray diffraction, scanning electron microscope-energy dispersive spectroscopy, and inductively coupled plasma-optical emission spectroscopy. The analysis results indicate that REO_x and SrO_x can be easily chlorinated from the simulated fuels; however, only a few of U oxide phases is chlorinated, particularly from the U/SrO_x-simulated fuels.

• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1236-1249
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• 2021

Although there are still controversial opinions and uncertainty on application of SiC_f/SiC composite cladding as next-generation cladding material for its great oxidation resistance in high temperature steam environment and other outstanding advantages, it cannot deny that SiC_f/SiC cladding is a potential accident tolerant fuel (ATF) cladding with high research priority and still in the engineering design stage for now. However, considering its disadvantages, such as low irradiated thermal conductivity, ductility that barely not exist, further evaluations of its in-pile behaviors are still necessary. Based on the self-developed code we recently updated, relevant thermohydraulic and mechanical models in FROBA-ATF were applied to simulate the cladding behaviors under normal and accident conditions in this paper. Even through steady-state performance analysis revealed that this kind of cladding material could greatly reduce the oxidation thickness, the thermal performance of UO₂-SiC was poor due to its low inpile thermal conductivity and creep rate. Besides, the risk of failure exists when reactor power decreased. With geometry optimization and dopant addition in pellets, the steady-state performance of UO₂-SiC was enhanced and the failure risk was reduced. The thermal and mechanical performance of the improved UO₂-SiC was further evaluated under Loss of coolant accident (LOCA) and Reactivity Initiated Accident (RIA) conditions. Transient results showed that the optimized ATF had better thermal performance, lower cladding hoop stress, and could provide more coping time under accident conditions.